Anterior Approach to Sacroiliac Joint

What it exposes. The anterior approach gives direct access to the anterior sacroiliac joint, the sacral ala and the inner table of the ilium for open reduction and plating of posterior SI joint disruptions that cannot be reduced closed, and for selected revision arthrodesis or anterior hardware problems. Access is via the lateral (iliac) window of the ilioinguinal approach, or a modified Stoppa, elevating iliacus off the inner table to reach the anterior SI joint and sacral ala. Why anterior (and not posterior or percutaneous). Most SI pathology is now managed posteriorly or percutaneously because those routes are simpler, safer and give better screw purchase. The anterior approach is reserved for the small subset that need direct visualisation of the anterior joint and the L5 nerve root, placement of an anterior column plate from ilium to sacrum, or address of anterior soft-tissue problems such as scarring or nerve entrapment. It is technically demanding and not a routine exposure - reserve it for complex revision cases performed by experienced pelvic surgeons. Indications.

• Irreducible posterior SI disruption needing open anterior reduction (the classic absolute indication)
• Failed posterior SI fusion with pseudarthrosis and persistent instability in a high-demand patient
• Revision SI arthrodesis after posterior-only fusion has failed
• Prominent anterior SI screws or hardware causing nerve compression or vascular compromise, requiring removal
• Selected anterior column / pelvic ring ORIF in vertical-shear (APC III, LC III) injuries with anterior SI disruption
• L5 nerve root decompression (compressed by callus, hardware or scar) and excision of heterotopic ossification around the joint Relative indications and contraindications. Relative: tumour resection involving the anterior SI joint. Avoid the anterior approach when posterior or percutaneous fixation is feasible, in active infection over the field, when the patient is unfit for prolonged complex pelvic surgery, in severe obesity (BMI more than 40), after pelvic radiotherapy (poor tissue quality), or in marked osteoporosis (poor screw purchase). Pre-operative assessment. Document baseline L5 (extensor hallucis longus, ankle dorsiflexion, dorsal foot sensation) and S1 (ankle plantarflexion, sole sensation) function carefully - these are the roots at risk and the baseline against which any post-operative deficit is judged. Image with an AP pelvis, inlet and outlet views (a Ferguson view - AP with 30 degrees of cephalad tilt - best shows the SI joint), a fine-cut CT (1mm slices) with 3D reconstruction to define joint morphology, nonunion, bone quality and hardware position, and MRI where infection, nerve entrapment or marrow oedema are in question; consider CT angiography in scarred revisions to map aberrant iliac anatomy. Position, setup and equipment. Supine on a radiolucent table, with a bump under the ipsilateral buttock (15-20 degrees) and the hip slightly flexed and externally rotated to open the joint; arms tucked or out on boards; C-arm access from multiple angles is essential. General anaesthesia with muscle relaxation, arterial line for revisions, tranexamic acid 1g at induction, broad-spectrum antibiotics, cell saver and 4-6 units crossmatched with vascular surgery on standby. Surface landmarks are the ASIS and pubic tubercle (the two anchors of the ilioinguinal incision), the inguinal ligament, the iliac crest (graft harvest site), and the midline (umbilicus to pubis) for the Stoppa alternative; the SI joint itself lies deep and is localised with fluoroscopy.

Work through the ilioinguinal exposure in layers, developing the lateral then the middle window, mobilising the iliac vessels medially and shielding the L5/lumbosacral trunk before opening the joint lateral to it.

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Structures at risk, by layer

Intra-operative complications. The feared complications are L5/lumbosacral trunk injury - the commonest neurological problem, reported in up to about 5 percent in some series, usually a traction neuropraxia that recovers over 6-18 months but with permanent foot drop after complete transection reported - and iliac vessel injury (uncommon but potentially fatal haemorrhage, most often from the common iliac vein). Lumbosacral plexus injury and bowel or bladder injury (from adhesions in revision cases) are rare (each less than 1 to 3 percent). Quoted rates come from small, heterogeneous series and should be quoted as ranges, not precise figures. Managing an iliac vessel injury. Apply direct pressure with a pack for at least five minutes and do not lift it to look; call vascular surgery and activate the massive transfusion protocol (1:1:1 PRBC to FFP to platelets, tranexamic acid, calcium) through two large-bore cannulae and an arterial line. Extend the exposure (medially to a Stoppa or to a full laparotomy if needed) and gain proximal and distal control. A small tear (less than 1cm) is repaired with lateral venorrhaphy using 5-0 or 6-0 Prolene; a large or complex injury needs a patch venoplasty (saphenous vein or PTFE) or an interposition graft (femoral vein or PTFE), and ligation of the common iliac vein is a last resort that is acceptable in an unstable patient because collateral flow is usually adequate, at the cost of leg oedema managed with compression stockings. Internal iliac vein ligation is better tolerated than common iliac ligation. If the patient is in extremis despite resuscitation, pack the pelvis, close rapidly and return to theatre in 24-48 hours for definitive repair. Post-operatively, monitor in ICU for re-bleeding, thrombosis and compartment syndrome, with serial haemoglobin and distal perfusion checks. Extensile options and alternatives. Extend medially from the ilioinguinal to a modified Stoppa for more medial joint and ala access; the lateral window extends proximally along the iliac crest for graft and iliac-wing control. For most primary SI pathology the safer alternatives are percutaneous iliosacral screws (Routt) or a posterior open approach, which avoid this neurovascular corridor entirely. Closure and post-operative surveillance. Repair the capsule and pelvic floor, restore the iliac vessels to anatomic position, and close in layers over a deep drain. Post-operatively, watch in ICU with neurological checks every two hours for 24 hours (L5 and S1 function versus the documented baseline), protect with toe-touch weight bearing for 6-8 weeks, advance to partial then full weight bearing by 10-12 weeks if radiographs progress, and assess fusion with CT at 6-12 months. Outcome correlates strongly with the quality of reduction; revision arthrodesis carries a guarded prognosis.

• Open reduction and anterior plating of an irreducible posterior SI disruption (ilium-to-sacrum plate) - the classic indication.
• Revision SI arthrodesis after failed posterior fusion (joint preparation, bone graft, anterior plate).
• Removal of prominent anterior SI screws or hardware causing nerve or vascular compromise.
• Anterior column / pelvic ring ORIF in unstable vertical-shear or LC III injuries.
• L5 nerve root decompression (callus, hardware or scar) and excision of heterotopic ossification around the joint.
• Selected tumour resection involving the anterior SI joint.